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Author Topic: Need AGC time constants settings explained  (Read 823 times)
N3OYO
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Posts: 113




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« on: May 28, 2007, 03:10:33 PM »

Can someone explain the "AGC time constant" settings on my 746 Pro?..Default settings are (for SSB) 0.3 (fast)..2.0 (mid) and 6.0 (slow)..How should it be set? It's presently set to the default "slow" (for SSB)..Can someone explain this and maybe the proper setting(s)?
                     Thanks in advance..
                      73'..Tom  N3OYO
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AA4PB
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Posts: 12643




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« Reply #1 on: May 28, 2007, 05:08:19 PM »

Its basically a matter of how long it takes the AGC to decay after a strong signal leaves the air. For example if a steady carrier was on an reading S9 and it suddenly switched off, how long would it take for the S meter to drop and the receiver sensitivity to recover.

For SSB you generally want a slow decay so that you don't have noise bursts between the words. The AGC holds the receiver sensitivity at the reduced value between words.

For break-in CW you want a faster AGC so that the receiver recovers fast enough for you to hear weak signals between characters.

For modes like Amtor and Pactor you want a fast AGC so that your receiver can recover quickly to receive the acknowlegements from the other station between your packets.

For modes like PSK31 that require a very linear signal chain you generally want a slow AGC so that it doesn't try to "follow" and compress (distort) the amplitude of the received signal.

The actual values are often a personal preference obtained by experimenting. Most likely the factory defaults are a good place to start (and where mine remains).
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N3OYO
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Posts: 113




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« Reply #2 on: May 28, 2007, 05:33:23 PM »

Thanks!
  73'...Tom N3OYO
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WB2WIK
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Posts: 20540




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« Reply #3 on: May 30, 2007, 02:20:54 PM »

The numerals express footlongs per fortnight and are rounded to the nearest ft/fn.

:-)

I love this technical stuff!
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AB3EO
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Posts: 25




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« Reply #4 on: May 31, 2007, 11:08:25 AM »

WIK,

I think you mean furlongs per fortnight, which is actually a measure of speed. The default settings are time measures. They are approximately microfortnights.

Other than that PB explained AGC speed settings very well.

Rich
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EXWA2SWA
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Posts: 158




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« Reply #5 on: May 31, 2007, 11:17:11 AM »

Nope - Steve meant footlongs. He's a transplanted Jersey guy who may (or may not) have memories of Rutt's Hut hot dogs.
73,
Jim NS5M
Also originally a Jersey guy
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K7MDO
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Posts: 325




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« Reply #6 on: June 18, 2007, 04:12:58 PM »

Great response and very useful to me as well.... thanks for taking the time and effort to explain this. 73, Tom
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